Hydrocarbon streams are refined through various unit operations to produce various types of fuel, industrial raw materials that are employed in production of other compounds or products, and petroleum-based products. Production of gasoline is a particularly important industrial process involving refining of hydrocarbons through various unit operations, including isomerization and catalytic reforming. Reforming of hydrocarbons is useful to convert paraffins to aromatic compounds in the presence of noble metal catalysts. Aromatic compounds provide high octane value and, thus, are desirable components in gasoline. Isomerization is effective to convert linear hydrocarbons into branched hydrocarbons, which have a higher octane value than linear compounds but a lower octane value than aromatic compounds. Isomerized streams (or isomerate) is substantially free of aromatic compounds, whereas reformate streams (or reformate) generally include high quantities of aromatic compounds (e.g., at least 50 wt %).
During refining, a hydrocarbon stream is generally separated into various streams based on the number of carbon atoms of compounds within each stream. Hydrocarbons having 7 or more carbon atoms are generally subject to reforming because reforming generally results in higher octane value than isomerization of these hydrocarbons. Hydrocarbons having 5 or 6 carbon atoms are generally subjected to isomerization.
Modern specifications for gasoline typically place limits on aromatic content. The limits on aromatic content restrict the amount of reformate that can be blended into the gasoline. Since refineries generally produce significantly more hydrocarbons having 7 or more carbon atoms, there is typically too much reformate produced relative to isomerate for cases where aromatics are highly restricted in gasoline. Hydrocarbons having 7 carbon atoms cannot be effectively isomerized with hydrocarbons having 5 or 6 carbon atoms, since hydrocarbons having 7 carbon atoms are subjected to cracking under conditions necessary to effectively isomerize hydrocarbons having 5 or 6 carbon atoms.
Accordingly, it is desirable to provide apparatuses and processes for isomerizing hydrocarbons that enable hydrocarbons having 5 or 6 carbon atoms and hydrocarbons having 7 carbon atoms to be separately and effectively isomerized. Furthermore, other desirable features and characteristics of the present subject matter will become apparent from the subsequent detailed description of the subject matter and the appended claims, taken in conjunction with the accompanying drawings and this background of the subject matter.